Mini-Encyclopedia of Papermaking Wet-End
Chemistry Additives
and Ingredients, their Composition, Functions, Strategies for Use

WHITE PITCH

Composition: The major component of "white pitch" sometimes
observed in paper machine systems is latex binder from recycled coated broke.
This can include styrene-butadiene resin (SBR), acrylic resins, and polyvinylacetate
latex components. It also can contain the associated coating pigments, including
clay, plastic pigments, calcium carbonate,
and titanium dioxide. White pitch problems are often
made more difficult due to mixing with wood resins, defoamer
components, and other tacky materials in the furnish.

Function: White pitch can cause reduced papermaking efficiency due to
felt filling and down-time required to clean up equipment.

Strategies for Use: It is highly recommended to do a chemical analysis.
This may make it possible to determine the most likely root causes of the problem.
One of the most general strategies for avoiding pitch problems is to keep the
tacky materials bound to the fibers. This is one of the ideas behind a common
practice of adding alum during or immediately after mechanical
pulping. The alum complexes with any soaps of resin acids and fatty acids, and
the presence of these complexes can serve to bind the multi-component droplets
of pitch to the fiber surfaces. Addition of highly cationic polymers such as
polyethyleneimine (PEI) to the process can have a similar
effect. The relative turbidity of filtrate obtained from different points in
the process can be used as an indication of the probable effectiveness of such
treatments with cationic materials. It is very common also to add talc
or another detackifying agent to coat tacky particles and minimize their tendency
to form large agglomerates, deposits, or spots in the product. An effective
retention aid system can help limit the filling of press
felts with pitch.

Cautions: Safe procedures must be followed when collecting samples of
pitch deposits. Equipment must be locked out and the air quality checked by
qualified people before entering enclosed areas such as headboxes.

PLEASE NOTE: Users of the information contained on these pages assume complete
responsibility to make sure that their practices are safe and do not infringe
upon an existing patent. There has been no attempt here to give full safety
instructions or to make note of all relevant patents governing the use of additives.
Please send corrections if you find errors or points that need better clarification.